The activation sequence of cellular protein handling systems after proteasomal inhibition in dopaminergic cells

Nuclear receptor coactivator 6 is a critical regulator of NLRP3 inflammasome activation and gouty arthritis

Transcriptional coactivators regulate the rate of gene expression in the nucleus. Nuclear receptor coactivator 6 (NCOA6), a coactivator, has been implicated in embryonic development, metabolism, and cancer pathogenesis, but its role in innate immunity and inflammatory diseases remains unclear. Here, we demonstrated that NCOA6 was expressed in monocytes and macrophages and that its level was increased under proinflammatory conditions. Unexpectedly, nuclear NCOA6 was found to translocate to the cytoplasm in activated monocytes and then become incorporated into the inflammasome with NLRP3 and ASC, forming cytoplasmic specks. Mechanistically, NCOA6 associated with the ATP hydrolysis motifs in the NACHT domain of NLRP3, promoting the oligomerization of NLRP3 and ASC and thereby instigating the production of IL-1β and active caspase-1. Of note, Ncoa6 deficiency markedly inhibited NLRP3 hyperactivation caused by the Nlrp3R258W gain-of-function mutation in macrophages. Genetic ablation of Ncoa6 substantially attenuated the severity of two NLRP3-dependent diseases, folic-induced acute tubular necrosis and crystal-induced arthritis, in mice. Consistent with these findings, NCOA6 was highly expressed in macrophages derived from gout patients, and NCOA6-positive macrophages were significantly enriched in gout macrophages according to the transcriptome profiling results. Conclusively, NCOA6 is a critical regulator of NLRP3 inflammasome activation and is therefore a promising target for NLRP3-dependent diseases, including gout.

Genetic diversity, transcript heterogeneity and allele mining of TaSKP1-6B-4 gene variants across diverse genotypes under terminal heat stress and genome wide characterization of TaSKP1 gene family from bread wheat (Triticum aestivum L.)

SKP1 (S-phase kinase protein1) is an essential regulatory component of SCF (Skp1-cullin-F-box) E3 ubiquitin ligases involved in maintenance of cellular protein homeostasis through ubiquitin mediated proteasome system (UPS). UPS play a key role in stress response and grain yield. Earlier, we isolated TaSKP1-6B-4, highly induced in flag leaf tissues (Accession No. KJ830759.1) of developing wheat caryopses under heat stress. To further assess the functional role of SKP1, genetic variability analysis was carried out in a panel of 25 contrasting germplasm through extensive phenotyping and transcript profiling of TaSKP1-6B-4 during anthesis under ambient and terminal heat stress (THS) in field experiments for two consecutive years. The analysis of variance revealed significant variations for all the traits studied. Higher H2(%), GCV, PCV, GA and GA% mean observed in tiller number per plant (23.81, 17.65, 5.71, 28, 30.86%) and grain number per head (30.27, 82.79, 60.16, 105.00, 108.64%) under THS over ambient temperature. Higher fold induction of TaSKP1-6B-4 transcripts was recorded in 10 genotypes viz. HD2967 (9.9), IC145456 (6.18) in flag leaf; while C-306 (15.88), RAJ3765 (8.37) in ear head. Allele mining of SKP1-6B-4 showed genotypic sequence variations. Whole genome wide search of SKP1 gene family identified 95 SKP1 genes which were structurally characterized. Grain yield, leaf senescence and other agronomic-morpho-physiological parameters combined with transcript profiling, cvHD2967, was found to be the best positively responsive to THS which by pedigree was not heat tolerant. We report a novel 2 year comprehensive field based analysis on collective genetic variability and SKP1/UPS modulation under a natural environmental setting. The data reveals potential functional role of UPS under THS and tolerant cultivars can be further utilized for clarifying the role of UPS mechanistically at the molecular level and for developing terminal heat stress tolerant wheat.

AGAP1-associated endolysosomal trafficking abnormalities link gene-environment interactions in neurodevelopmental disorders

AGAP1 is an Arf1 GTPase-activating protein that regulates endolysosomal trafficking. Damaging variants have been linked to cerebral palsy and autism. We report three new cases in which individuals had microdeletion variants in AGAP1. The affected individuals had intellectual disability (3/3), autism (3/3), dystonia with axial hypotonia (1/3), abnormalities of brain maturation (1/3), growth impairment (2/3) and facial dysmorphism (2/3). We investigated mechanisms potentially underlying AGAP1 variant-mediated neurodevelopmental impairments using the Drosophila ortholog CenG1a. We discovered reduced axon terminal size, increased neuronal endosome abundance and elevated autophagy compared to those in controls. Given potential incomplete penetrance, we assessed gene-environment interactions. We found basal elevation in the phosphorylation of the integrated stress-response protein eIF2α (or eIF2A) and inability to further increase eIF2α phosphorylation with subsequent cytotoxic stressors. CenG1a-mutant flies had increased lethality from exposure to environmental insults. We propose a model wherein disruption of AGAP1 function impairs endolysosomal trafficking, chronically activating the integrated stress response and leaving AGAP1-deficient cells susceptible to a variety of second-hit cytotoxic stressors. This model may have broader applicability beyond AGAP1 in instances where both genetic and environmental insults co-occur in individuals with neurodevelopmental disorders.

AGAP1-associated endolysosomal trafficking abnormalities link gene-environment interactions in a neurodevelopmental disorder

AGAP1 is an Arf1 GAP that regulates endolysosomal trafficking. Damaging variants have been linked to cerebral palsy and autism. We report 3 new individuals with microdeletion variants in AGAP1 . Affected individuals have intellectual disability (3/3), autism (3/3), dystonia with axial hypotonia (1/3), abnormalities of brain maturation (1/3), growth impairment (2/3) and facial dysmorphism (2/3). We investigated mechanisms potentially underlying AGAP1 neurodevelopmental impairments using the Drosophila ortholog, CenG1a . We discovered reduced axon terminal size, increased neuronal endosome abundance, and elevated autophagy at baseline. Given potential incomplete penetrance, we assessed gene-environment interactions. We found basal elevation in phosphorylation of the integrated stress-response protein eIF2α and inability to further increase eIF2α-P with subsequent cytotoxic stressors. CenG1a -mutant flies have increased lethality from exposure to environmental insults. We propose a model wherein disruption of AGAP1 function impairs endolysosomal trafficking, chronically activating the integrated stress response, and leaving AGAP1-deficient cells susceptible to a variety of second hit cytotoxic stressors. This model may have broader applicability beyond AGAP1 in instances where both genetic and environmental insults co-occur in individuals with neurodevelopmental disorders.

Summary statement

We describe 3 additional patients with heterozygous AGAP1 deletion variants and use a loss of function Drosophila model to identify defects in synaptic morphology with increased endosomal sequestration, chronic autophagy induction, basal activation of eIF2α-P, and sensitivity to environmental stressors.

The cytotoxic concentration of rosmarinic acid increases MG132-induced cytotoxicity, proteasome inhibition, autophagy, cellular stresses, and apoptosis in HepG2 cells

Rosmarinic acid (RA) is a natural polyphenolic compound derived from many common herbal plants. Although it is known that RA has many important biological activities, its effect on proteasome inhibitor-induced changes in cancer treatment or its effects on any experimental proteasome inhibition model is unknown. The aim of the study was to investigate the effect of RA on MG132-induced cytotoxicity, proteasome inhibition, autophagy, cellular stresses, and apoptosis in HepG2 cells. HepG2 cells were treated with 10, 100, and 1000 µM RA in the presence of MG132 for 24 h; 10 and 100 µM RA did not affect but 1000 µM RA decreased cell viability in HepG2 cells. MG132 caused a significant decrease in cell viability and phosphorylation of mammalian target of rapamycin and a significant increase in levels of polyubiquitinated protein, microtubule-associated proteins 1A/1B light chain 3B-II (LC3B-II), heat shock protein 70 (HSP70), binding immunoglobulin protein (BiP), activating transcription factor 4 (ATF4), protein carbonyl, and cleaved poly(adenosine diphosphate-ribose) polymerase 1 (PARP1); 10 and 100 µM RA did not significantly change these effects of MG132 in HepG2 cells; 1000 µM RA caused a significant decrease in cell viability and a significant increase in polyubiquitinated protein, LC3B-II, HSP70, BiP, ATF4, protein carbonyl, and cleaved PARP1 levels in MG132-treated cells. Our study showed that only 1000 µM RA increased MG132-induced cytotoxicity, proteasome inhibition, autophagy, cellular stresses, and apoptosis in HepG2 cells. According to our results, cytotoxic concentration of RA can potentiate the effects of MG132 in hepatocellular carcinoma treatment.

Pueraria lobata and Daidzein Reduce Cytotoxicity by Enhancing Ubiquitin-Proteasome System Function in SCA3-iPSC-Derived Neurons

Spinocerebellar ataxia type 3 (SCA3) is an autosomal dominant neurodegenerative disorder caused by a CAG repeat expansion within the ATXN3/MJD1 gene. The expanded CAG repeats encode a polyglutamine (polyQ) tract at the C-terminus of the ATXN3 protein. ATXN3 containing expanded polyQ forms aggregates, leading to subsequent cellular dysfunctions including an impaired ubiquitin-proteasome system (UPS). To investigate the pathogenesis of SCA3 and develop potential therapeutic strategies, we established induced pluripotent stem cell (iPSC) lines from SCA3 patients (SCA3-iPSC). Neurons derived from SCA3-iPSCs formed aggregates that are positive to the polyQ marker 1C2. Treatment with the proteasome inhibitor, MG132, on SCA3-iPSC-derived neurons downregulated proteasome activity, increased production of radical oxygen species (ROS), and upregulated the cleaved caspase 3 level and caspase 3 activity. This increased susceptibility to the proteasome inhibitor can be rescued by a Chinese herbal medicine (CHM) extract NH037 (from Pueraria lobata) and its constituent daidzein via upregulating proteasome activity and reducing protein ubiquitination, oxidative stress, cleaved caspase 3 level, and caspase 3 activity. Our results successfully recapitulate the key phenotypes of the neurons derived from SCA3 patients, as well as indicate the potential of NH037 and daidzein in the treatment for SCA3 patients.

Myocyte-Damaging Effects and Binding Kinetics of Boronic Acid and Epoxyketone Proteasomal-Targeted Drugs

The proteasome inhibitors bortezomib, carfilzomib, and ixazomib, which are used in the treatment of multiple myeloma have greatly improved response rates. Several other proteasome inhibitors, including delanzomib and oprozomib, are in clinical trials. Carfilzomib and oprozomib are epoxyketones that form an irreversible bond with the 20S proteasome, whereas bortezomib, ixazomib, and delanzomib are boronic acids that form slowly reversible adducts. Several of the proteasome inhibitors have been shown to exhibit specific cardiac toxicities. A primary neonatal rat myocyte model was used to study the relative myocyte-damaging effects of five proteasome inhibitors with a view to identifying potential class differences and the effect of inhibitor binding kinetics. Bortezomib was shown to induce the most myocyte damage followed by delanzomib, ixazomib, oprozomib, and carfilzomib. The sensitivity of myocytes to proteasome inhibitors, which contain high levels of chymotrypsin-like proteasomal activity, may be due to inhibition of proteasomal-dependent ongoing sarcomeric protein turnover. All inhibitors inhibited the chymotrypsin-like proteasomal activity of myocyte lysate in the low nanomolar concentration range and exhibited time-dependent inhibition kinetics characteristic of slow-binding inhibitors. Progress curve analysis of the inhibitor concentration dependence of the slow-binding kinetics was used to measure second-order "on" rate constants for binding. The second-order rate constants varied by 90-fold, with ixazomib reacting the fastest, and oprozomib the slowest. As a group, the boronic acid drugs were more damaging to myocytes than the epoxyketone drugs. Overall, inhibitor-induced myocyte damage was positively, but not significantly, correlated with their second-order rate constants.

Molecular Mechanisms of the Cardiotoxicity of the Proteasomal-Targeted Drugs Bortezomib and Carfilzomib

Bortezomib and carfilzomib are anticancer drugs that target the proteasome. However, these agents have been shown to exhibit some specific cardiac toxicities by as yet unknown mechanisms. Bortezomib and carfilzomib are also being used clinically in combination with doxorubicin, which is also cardiotoxic. A primary neonatal rat myocyte model was used to study these cardiotoxic mechanisms. Exposure to submicromolar concentrations of bortezomib and carfilzomib resulted in significant myocyte damage and induced apoptosis. Both bortezomib and carfilzomib inhibited the chymotrypsin-like proteasomal activity of myocyte lysate in the low nanomolar concentration range and exhibited time-dependent inhibition kinetics. The high sensitivity of myocytes, which were determined to contain high specific levels of chymotrypsin-like proteasomal activity, to the damaging effects of bortezomib and carfilzomib was likely due to the inhibition of proteasomal-dependent ongoing sarcomeric protein turnover. A brief preexposure of myocytes to non-toxic nanomolar concentrations of bortezomib or carfilzomib greatly increased doxorubicin-mediated damage, which suggests that the combination of doxorubicin with either bortezomib or carfilzomib may produce more than additive cardiotoxicity. The doxorubicin cardioprotective agent dexrazoxane partially protected myocytes from doxorubicin plus bortezomib or carfilzomib treatment, in spite of the fact that bortezomib and carfilzomib inhibited the dexrazoxane-induced decreases in topoisomerase IIβ protein levels in myocytes. These latter results suggest that the doxorubicin cardioprotective effects of dexrazoxane and the doxorubicin-mediated cardiotoxicity were not exclusively due to targeting of topoisomerase IIβ.

Effect of isothiocyanates, BITC and PEITC, on stress protein accumulation, protein aggregation and aggresome-like structure formation in Xenopus A6 kidney epithelial cells

Numerous studies have elucidated the health benefits of organosulfur compounds, known as isothiocyanates (ITCs), derived from cruciferous vegetables. As electrophiles, ITCs have the ability to directly bind and modify thiol-containing compounds such as glutathione and cellular protein, including tubulin. While the biochemical effects of ITCs have been well characterized, less information is available regarding their effects on the accumulation of stress-inducible heme oxygenase-1 (HO-1), heat shock proteins (HSPs) and the possible formation of aggregated protein due to thiol modification. The present study has examined the effect of the ITCs, benzyl isothiocyanate (BITC) and phenethyl isothiocyanate (PEITC), on the accumulation of HO-1, HSP70 and HSP30 in Xenopus laevis A6 kidney epithelial cells. Immunoblot analysis revealed that both BITC and PEITC induced the accumulation of HO-1 and HSP70 whereas HSP30 levels were enhanced only in cells treated with BITC. Immunocytochemistry determined that ITC treatment induced F-actin disorganization and membrane ruffling and enhanced accumulation of HO-1 in the cytoplasm. Additionally, BITC induced enhanced levels of ubiquitinated protein, aggregated protein, and the collapse and fragmentation of microtubules. In comparison, treatment of cells with the proteasomal inhibitor, MG132, induced the accumulation of all three stress proteins, aggregated protein and aggresome-like structures. Finally, cells pretreated with BITC inhibited the formation of MG132-induced aggresome-like structures in the perinuclear region. This latter finding suggests that BITC-induced microtubule fragmentation may impede the movement of aggregated protein via microtubules and their subsequent coalescence into aggresome-like structures in the perinuclear region.

The burden of trisomy 21 disrupts the proteostasis network in Down syndrome

Down syndrome (DS) is a genetic disorder caused by trisomy of chromosome 21. Abnormalities in chromosome number have the potential to lead to disruption of the proteostasis network (PN) and accumulation of misfolded proteins. DS individuals suffer from several comorbidities, and we hypothesized that disruption of proteostasis could contribute to the observed pathology and decreased cell viability in DS. Our results confirm the presence of a disrupted PN in DS, as several of its elements, including the unfolded protein response, chaperone system, and proteasomal degradation exhibited significant alterations compared to euploid controls in both cell and mouse models. Additionally, when cell models were treated with compounds that promote disrupted proteostasis, we observed diminished levels of cell viability in DS compared to controls. Collectively our findings provide a cellular-level characterization of PN dysfunction in DS and an improved understanding of the potential pathogenic mechanisms contributing to disrupted cellular physiology in DS. Lastly, this study highlights the future potential of designing therapeutic strategies that mitigate protein quality control dysfunction.

Re-Cloning the N27 Dopamine Cell Line to Improve a Cell Culture Model of Parkinson's Disease

Parkinson's disease is characterized by the death of dopaminergic neurons in the substantia nigra. To understand the molecular mechanisms of the disease, an in vitro model is important. In the 1990s, we used the SV40 large T antigen to immortalize dopaminergic neurons derived from Embryonic Day 14 rat mesencephalon. We selected a clone for its high expression of dopaminergic neuron markers such as tyrosine hydroxylase (TH), and we named it 1RB3AN27 (N27). Because the original N27 cell line has been passaged many times, the line has become a mixture of cell types with highly variable expression of TH. In the current study, we have performed multiple rounds of clonal cultures and have identified a dopaminergic cell clone expressing high levels of TH and the dopamine transporter (DAT). We have named this new clone N27-A. Nearly 100% of N27-A cells express TH, DAT and Tuj1. Western blots have confirmed that N27-A cells have three to four times the levels of TH and DAT compared to the previous mixed population in N27. Further analysis has shown that the new clone expresses the dopamine neuron transcription factors Nurr1, En1, FoxA2 and Pitx3. The N27-A cells express the vesicular monoamine transporter (VMAT2), but do not express dopamine-beta-hydroxylase (DβH), the enzyme responsible for converting dopamine to norepinephrine. Functional analysis has shown that N27-A cells are more sensitive than N27 cells to neurotoxins taken up by the dopamine transporter such as 6-hydroxydopamine and 1-methyl-4-phenylpyridine (MPP+). The DAT inhibitor nomifensine can block MPP+ induced toxicity. The non-selective toxic effects of hydrogen peroxide were similar in both cell lines. The N27-A cells show dopamine release under basal and depolarization conditions. We conclude that the new N27-A clone of the immortalized rat dopaminergic cell line N27 should provide an improved in vitro model for Parkinson's disease research.

Cigarette smoke-induced autophagy impairment accelerates lung aging, COPD-emphysema exacerbations and pathogenesis

Cigarette-smoke (CS) exposure and aging are the leading causes of chronic obstructive pulmonary disease (COPD)-emphysema development, although the molecular mechanism that mediates disease pathogenesis remains poorly understood. Our objective was to investigate the impact of CS exposure and aging on autophagy and the pathophysiological changes associated with lung aging (senescence) and emphysema progression. Beas2b cells, C57BL/6 mice, and human (GOLD 0-IV) lung tissues were used to determine the central mechanism involved in CS/age-related COPD-emphysema pathogenesis. Beas2b cells and murine lungs exposed to cigarette smoke extract (CSE)/CS showed a significant ( P < 0.05) accumulation of poly-ubiquitinated proteins and impaired autophagy marker, p62, in aggresome bodies. Moreover, treatment with the autophagy-inducing antioxidant drug cysteamine significantly ( P < 0.001) decreased CSE/CS-induced aggresome bodies. We also found a significant ( P < 0.001) increase in levels of aggresome bodies in the lungs of smokers and COPD subjects in comparison to nonsmoker controls. Furthermore, the presence and levels of aggresome bodies statistically correlated with severity of emphysema and alveolar senescence. In addition to CS exposure, lungs from old mice also showed accumulation of aggresome bodies, suggesting this as a common mechanism to initiate cellular senescence and emphysema. Additionally, Beas2b cells and murine lungs exposed to CSE/CS showed cellular apoptosis and senescence, which were both controlled by cysteamine treatment. In parallel, we evaluated the impact of CS on pulmonary exacerbation, using mice exposed to CS and/or infected with Pseudomonas aeruginosa ( Pa), and confirmed cysteamine's potential as an autophagy-inducing antibacterial drug, based on its ability to control CS-induced pulmonary exacerbation ( Pa-bacterial counts) and resulting inflammation. CS induced autophagy impairment accelerates lung aging and COPD-emphysema exacerbations and pathogenesis.

Nanomedicine and nanotoxicology: the pros and cons for neurodegeneration and brain cancer

Current strategies for brain diseases are mostly symptomatic and noncurative. Nanotechnology has the potential to facilitate the transport of drugs across the blood-brain barrier and to enhance their pharmacokinetic profile. However, to reach clinical application, an understanding of nanoneurotoxicity in terms of oxidative stress and inflammation is required. Emerging evidence has also shown that nanoparticles have the ability to alter autophagy, which can induce inflammation and oxidative stress, or vice versa. These effects may increase neurodegenerative processes damage, but on the other hand, they may have benefits for brain cancer therapies. In this review, we emphasize how nanomaterials may induce neurotoxic effects focusing on neurodegeneration, and how these effects could be exploited toward brain cancer treatment.

Role of Cigarette Smoke-Induced Aggresome Formation in Chronic Obstructive Pulmonary Disease-Emphysema Pathogenesis

Cigarette smoke (CS) exposure is known to induce proteostasis imbalance that can initiate accumulation of ubiquitinated proteins. Therefore, the primary goal of this study was to determine if first- and secondhand CS induces localization of ubiquitinated proteins in perinuclear spaces as aggresome bodies. Furthermore, we sought to determine the mechanism by which smoke-induced aggresome formation contributes to chronic obstructive pulmonary disease (COPD)-emphysema pathogenesis. Hence, Beas2b cells were treated with CS extract (CSE) for in vitro experimental analysis of CS-induced aggresome formation by immunoblotting, microscopy, and reporter assays, whereas chronic CS-exposed murine model and human COPD-emphysema lung tissues were used for validation. In preliminary analysis, we observed a significant (P < 0.01) increase in ubiquitinated protein aggregation in the insoluble protein fraction of CSE-treated Beas2b cells. We verified that CS-induced ubiquitin aggregrates are localized in the perinuclear spaces as aggresome bodies. These CS-induced aggresomes (P < 0.001) colocalize with autophagy protein microtubule-associated protein 1 light chain-3B(+) autophagy bodies, whereas U.S. Food and Drug Administration-approved autophagy-inducing drug (carbamazepine) significantly (P < 0.01) decreases their colocalization and expression, suggesting CS-impaired autophagy. Moreover, CSE treatment significantly increases valosin-containing protein-p62 protein-protein interaction (P < 0.0005) and p62 expression (aberrant autophagy marker; P < 0.0001), verifying CS-impaired autophagy as an aggresome formation mechanism. We also found that inhibiting protein synthesis by cycloheximide does not deplete CS-induced ubiquitinated protein aggregates, suggesting the role of CS-induced protein synthesis in aggresome formation. Next, we used an emphysema murine model to verify that chronic CS significantly (P < 0.0005) induces aggresome formation. Moreover, we observed that autophagy induction by carbamazepine inhibits CS-induced aggresome formation and alveolar space enlargement (P < 0.001), confirming involvement of aggresome bodies in COPD-emphysema pathogenesis. Finally, significantly higher p62 accumulation in smokers and severe COPD-emphysema lungs (Global Initiative for Chronic Obstructive Lung Disease Stage III/IV) as compared with normal nonsmokers (Global Initiative for Chronic Obstructive Lung Disease Stage 0) substantiates the pathogenic role of autophagy impairment in aggresome formation and COPD-emphysema progression. In conclusion, CS-induced aggresome formation is a novel mechanism involved in COPD-emphysema pathogenesis.

A Novel Hsp90 Inhibitor Activates Compensatory Heat Shock Protein Responses and Autophagy and Alleviates Mutant A53T α-Synuclein Toxicity

A potential cause of neurodegenerative diseases, including Parkinson's disease (PD), is protein misfolding and aggregation that in turn leads to neurotoxicity. Targeting Hsp90 is an attractive strategy to halt neurodegenerative diseases, and benzoquinone ansamycin (BQA) Hsp90 inhibitors such as geldanamycin (GA) and 17-(allylamino)-17-demethoxygeldanamycin have been shown to be beneficial in mutant A53T α-synuclein PD models. However, current BQA inhibitors result in off-target toxicities via redox cycling and/or arylation of nucleophiles at the C19 position. We developed novel 19-substituted BQA (19BQA) as a means to prevent arylation. In this study, our data demonstrated that 19-phenyl-GA, a lead 19BQA in the GA series, was redox stable and exhibited little toxicity relative to its parent quinone GA in human dopaminergic SH-SY5Y cells as examined by oxygen consumption, trypan blue, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide (MTT), and apoptosis assays. Meanwhile, 19-phenyl-GA retained the ability to induce autophagy and potentially protective heat shock proteins (HSPs) such as Hsp70 and Hsp27. We found that transduction of A53T, but not wild type (WT) α-synuclein, induced toxicity in SH-SY5Y cells. 19-Phenyl-GA decreased oligomer formation and toxicity of A53T α-synuclein in transduced cells. Mechanistic studies indicated that mammalian target of rapamycin (mTOR)/p70 ribosomal S6 kinase signaling was activated by A53T but not WT α-synuclein, and 19-phenyl-GA decreased mTOR activation that may be associated with A53T α-synuclein toxicity. In summary, our results indicate that 19BQAs such as 19-phenyl-GA may provide a means to modulate protein-handling systems including HSPs and autophagy, thereby reducing the aggregation and toxicity of proteins such as mutant A53T α-synuclein.

Quinone-induced protein handling changes: implications for major protein handling systems in quinone-mediated toxicity

Para-quinones such as 1,4-Benzoquinone (BQ) and menadione (MD) and ortho-quinones including the oxidation products of catecholamines, are derived from xenobiotics as well as endogenous molecules. The effects of quinones on major protein handling systems in cells; the 20/26S proteasome, the ER stress response, autophagy, chaperone proteins and aggresome formation, have not been investigated in a systematic manner. Both BQ and aminochrome (AC) inhibited proteasomal activity and activated the ER stress response and autophagy in rat dopaminergic N27 cells. AC also induced aggresome formation while MD had little effect on any protein handling systems in N27 cells. The effect of NQO1 on quinone induced protein handling changes and toxicity was examined using N27 cells stably transfected with NQO1 to generate an isogenic NQO1-overexpressing line. NQO1 protected against BQ-induced apoptosis but led to a potentiation of AC- and MD-induced apoptosis. Modulation of quinone-induced apoptosis in N27 and NQO1-overexpressing cells correlated only with changes in the ER stress response and not with changes in other protein handling systems. These data suggested that NQO1 modulated the ER stress response to potentiate toxicity of AC and MD, but protected against BQ toxicity. We further demonstrated that NQO1 mediated reduction to unstable hydroquinones and subsequent redox cycling was important for the activation of the ER stress response and toxicity for both AC and MD. In summary, our data demonstrate that quinone-specific changes in protein handling are evident in N27 cells and the induction of the ER stress response is associated with quinone-mediated toxicity.

Region-specific vulnerability to endoplasmic reticulum stress-induced neuronal death in rat brain after status epilepticus

We sought to clarify the involvement and the intra-cerebral distribution variability of C/EBP homologous protein (CHOP), a representative molecule related to endoplasmic reticulum (ER) stress-induced cell death signalling pathways, in neuronal death resulting from status epilepticus in rats. The expression patterns of CHOP and glucose-regulated protein (GRP) 78, a good marker of ER stress, were assessed by Western blotting, real-time PCR, Hoechst and immunohistochemistry in the hippocampus, cortex and striatum on a status epilepticus (SE) model. Double-fluorescent staining of CHOP and the terminal deoxynucleotidyl transferase-mediated DNA nick-end labelling (TUNEL) method were performed to clarify the involvement of CHOP in cell death. SE resulted in a timedependent increase in the expression of GRP78 and CHOP. The expression of GRP78 protein was increased at 3, 6 and 12 h after SE and no brain region variability was found. The expression of CHOP protein was also increased, reached its peak at 24 h and remained high at 48 h. CHOP protein expression, however, showed brain region variability with highest expression noted in the hippocampus followed by the striatum, and lowest in the cortex. The up-regulation of CHOP occurring at the transcriptional level was demonstrated by real-time PCR. Double fluorescence showed that CHOP expression strongly correlated with neurons undergoing apoptosis. The results indicated that SE compromises the function of the ER and that the hippocampus is more vulnerable than the cortex and the striatum.

Polycystin-1 negatively regulates Polycystin-2 expression via the aggresome/autophagosome pathway

Mutations of the PKD1 and PKD2 genes, encoding polycystin-1 (PC1) and polycystin-2 (PC2), respectively, lead to autosomal dominant polycystic kidney disease. Interestingly, up-regulation or down-regulation of PKD1 or PKD2 leads to polycystic kidney disease in animal models, but their interrelations are not completely understood. We show here that full-length PC1 that interacts with PC2 via a C-terminal coiled-coil domain regulates PC2 expression in vivo and in vitro by down-regulating PC2 expression in a dose-dependent manner. Expression of the pathogenic mutant R4227X, which lacks the C-terminal coiled-coil domain, failed to down-regulate PC2 expression, suggesting that PC1-PC2 interaction is necessary for PC2 regulation. The proteasome and autophagy are two pathways that control protein degradation. Proteins that are not degraded by proteasomes precipitate in the cytoplasm and are transported via histone deacetylase 6 (HDAC6) toward the aggresomes. We found that HDAC6 binds to PC2 and that expression of full-length PC1 accelerates the transport of the HDAC6-PC2 complex toward aggresomes, whereas expression of the R4227X mutant fails to do so. Aggresomes are engulfed by autophagosomes, which then fuse with the lysosome for degradation; this process is also known as autophagy. We have now shown that PC1 overexpression leads to increased degradation of PC2 via autophagy. Interestingly, PC1 does not activate autophagy generally. Thus, we have now uncovered a new pathway suggesting that when PC1 is expressed, PC2 that is not bound to PC1 is directed to aggresomes and subsequently degraded via autophagy, a control mechanism that may play a role in autosomal dominant polycystic kidney disease pathogenesis.

Implications for oxidative stress and astrocytes following 26S proteasomal depletion in mouse forebrain neurones

Neurodegenerative diseases are characterized by progressive degeneration of selective neurones in the nervous system, but the underlying mechanisms involved in neuroprotection and neurodegeneration remain unclear. Dysfunction of the ubiquitin proteasome system is one of the proposed hypotheses for the cause and progression of neuronal loss. We have performed quantitative two-dimensional fluorescence difference in-gel electrophoresis combined with peptide mass fingerprinting to reveal proteome changes associated with neurodegeneration following 26S proteasomal depletion in mouse forebrain neurones. Differentially expressed proteins were validated by Western blotting, biochemical assays and immunohistochemistry. Of significance was increased expression of the antioxidant enzyme peroxiredoxin 6 (PRDX6) in astrocytes, associated with oxidative stress. Interestingly, PRDX6 is a bifunctional enzyme with antioxidant peroxidase and phospholipase A2 (PLA2) activities. The PLA2 activity of PRDX6 was also increased following 26S proteasomal depletion and may be involved in neuroprotective or neurodegenerative mechanisms. This is the first in vivo report of oxidative stress caused directly by neuronal proteasome dysfunction in the mammalian brain. The results contribute to understanding neuronal-glial interactions in disease pathogenesis, provide an in vivo link between prominent disease hypotheses and importantly, are of relevance to a heterogeneous spectrum of neurodegenerative diseases.